This invention relates to a multi-layer sliding member having a back metal and a Cu--Zn-based alloy layer bonded together by a brazing (soldering) material (intermediate bonding layer), and also relates to a method of producing such a sliding member.
A casting method by use of gravity casting and a brazing method are commonly known as a conventional method of producing a multi-layer sliding member having a Cu--Zn-based alloy layer.
In a casting method by use of gravity, a solid-liquid coexistent temperature range available when casting a Cu--Zn-based alloy is narrow, and as compared with a Cu--Sn-based alloy and a Cu--Sn--Pb alloy, a casting defect such as a cavity (blow hole) and a crack is liable to develop in the cast Cu--Zn-based alloy. Another problem is that it is difficult to bond this alloy to a back metal in a stably manner, and therefore the kinds of alloys to be cast are limited. In a brazing method, an oxide film (passive film) of zinc on a Cu--Zn-based alloy adversely affects the wettability with a brazing material, and besides vapor of zinc occurs at high temperatures, so that an adequate bonding strength can not be obtained. Thus, it has been thought difficult to braze a Cu--Zn-based alloy.
In the conventional brazing method and a multi-layer sliding member produced by this method, there have been encountered problems that the wettability between the Cu--Zn-based alloy and the brazing material is poor, and that a defect, such as a blow hole and separation, develops, so that the bonding strength is very low.